1. Field of the Invention
The present invention relates to a saddle-stitching stapler.
2. Related Art
In a saddle-stitching stapler, a staple can be driven in an intermediate portion of sheets of paper. When the staple is driven in a fold of the sheets of paper, the sheets of paper are formed to a booklet. In the saddle-stitching stapler, generally, a driver for driving the staple, and a clincher for clinching leg portions of the driven staple which have penetrated through the sheets of paper are arranged apart in an up/down direction. As a method of clinching the leg portions of the staple in the saddle-stitching stapler, there are a movable clincher type and a fixed clincher type. In the movable clincher type, after the entirety of the staple leg portions has completely penetrated through the sheets of paper, a movable clincher rotates and the leg portions are clinched. In the fixed clincher type, immediately after leading ends of the staple leg portions have penetrated through the sheets of paper, the staple leg portions are guided into grooves of a clincher and clinched.
Of these two types, the fixed clincher type is used widely in an inexpensive low-speed finisher to an expensive high-speed finisher. The reason is that: since the fixed clincher type does not require a clincher actuating mechanism and has the simple structure, the cost can be held down and space reduction is enabled. Further, another reason is that: since technology of folding thick paper at one time has not been established yet, a stapler mounted on the finisher does not need an ability of stapling 25 to 30 or more paper sheets.
In the fixed clincher type, the leg portions of the staple driven out by the driver are taken in the clincher grooves and bent so as to form a straight line. Therefore, even in case that front/rear misalignment between the driver and the clincher occurs a little, disadvantages such as an inclination of the staple and overlap of the staple leg portions are not produced. Namely, an acceptable range relating to the front/rear misalignment between the driver and the clincher is wide. On the other hand, the clincher in the fixed clincher type is fixed and the clincher grooves are formed in the shape of bilateral symmetry. Therefore, in case that there is misalignment in a right/left direction between the driver and the clincher, even if its misalignment is small, the both-side leg portions bend unequally. Namely, when a leading end of one leg portion abuts on a high portion of a slant surface of one-sided clincher groove, a leading end of the other leg portion abuts on a lower portion on a slant surface of the other-sided clincher groove, so that the both leg portions are difficult to bend equally. Accordingly, in the fixed clincher type, an acceptable range relating to the right/left misalignment between the driver and the clincher is narrow. Thus, very sever accuracy is required for the right/left alignment between the driver and the clincher, and an ambitious jig and a complicated structure are required for alignment.
Further, in a finisher disclosed in JP-A-2000-185868, a driver and a clincher are movable in the right/left direction by respective timing belts (transport belts). In this finisher, it is intended that the both belts are laid around pulleys provided for the same axis thereby to move simultaneously the driver and the clincher in the same direction by the same amount.
However, in the structure in which both of the clincher and the driver are carried by the timing belts, it is difficult to keep a relative position between the clincher and the driver constant due to expansion and flexure of the timing belt. Therefore, for commercialization of a finisher of up/down separation type which adopts a fixed clincher and has moving mechanisms for a clincher and a driver, it is necessary to perform control by means of an expensive stepping motor in order to keep the relative position between the clincher and the driver constant. In result, an entire stapler becomes expensive, and it is very difficult for the stapler adopting the fixed clincher type to realize the structure in which the driver and clincher are moved in a separation manner.